The present invention relates to bean curd or tofu, and more particularly to an improvement in a method and an apparatus for manufacturing bean curd.
As wellknown in the art bean curd or tofu is usually industrially manufactured as follows:
Soybeans are first dipped in water for about 12 hours, and they are then ground to pasty state by e.g. a mill resulting in one kind of a slurry, i.e. so-callled "go" in accordance with the Japanese term. Thereafter, the slurry or "go" is heated with water being added thereto, and the heated slurry is squeezed while it is hot so that soybean milk is obtained, with the insolubles being separated out. When the soybean milk is cooled to a temperature of about 70.degree. C. calcium sulphate (CaSO.sub.4) as a coagulating agent is added thereto as an aqueous solution in a ratio of 2 to 3 wt % of the amount of the soybeans so that the protein contained in the soybean milk is coagulated. After completion of the coagulation, which usually takes about 10 minutes from the addition of the coagulating agent, the supernatant liquid is discarded and the coagulated substance is transferred into an open-topped rectangular box having a considerable depth which has the side walls and the bottom all appropriately formed with a number of small through holes, and which has its inner periphery previously covered entirely with cloth. After transfer, a weight is applied over the whole surface of the milk so that the water is discharged out of the box through the cloth and the through-holes, leaving the bean curd within the box.
Among the above processes the heating of the slurry has been usually carried out such that it is poured into an open-topped vessel and boiled therein from the beginning to the completion throughout by directly injecting heating steam into the slurry in a sufficient amount thereof. This makes it impossible to produce bean curd rich in protein, because such a conventional boiling process often destroys the soybean protein, and also deteriorates the yield of the bean curd, decreasing the rigidity, luster, fineness of grain, etc. of the product.